Tree's "item_activated" and "item_double_clicked" signals

[YeldhamDev]

Godot version:
ad5ac05

Issue description:
According with the docs, item_activated is emitted when an item is double clicked. However, there is a signal named item_double_clicked which says it does exactly the same thing.

I tested both, and seems that only item_activated is emitted, so what's the point of the other signal?

[akien-mga]

According to git blame it was added by @djrm in 70c9979, later modified by @volzhs.

[volzhs]

based on commit, item_activated is emitted when double click on label,
and item_double_clicked is emitted when double click on icon.

[YeldhamDev]

@volzhs I see. But neither the signal names or their descriptions even remotely imply that.

[volzhs]

need someone to update docs I think.
but... it's not me, not a native speaker.

[akien-mga]

Maybe we should start maintaining a new list for the stuff we'd like to rename the day where we'll allow ourselves to break compatibility. Edit: Done, see #16863.